<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <script type="text/javascript">
        var fun = function(){
            alert("无参函数")
        }

        fun = function(a,b){
            alert(a+" "+b);
        }

        fun();
    </script>
</head>
<body>

</body>
</html>